In rhetoric, 'ethos' is one of the three artistic proofs (pistis) modes of persuasion (other principles being logos and pathos) discussed by Aristotle in 'Rhetoric' as a component of argument. At first speakers must establish ethos. On the one hand, this can mean merely "moral competence", but Aristotle broadens this word to encompass expertise and knowledge.

Looks like the audience is trying to determine whether you are a high or a low-ethos poster. Why do you retort with the same argument ("my martial experience is irrelevant to the topic") over and over again? If you write things in a public forum, it is because you intend for people to read them, right? You have something to tell the world. So, if what you write relates to budo, why wouldn't the readers wonder about your qualifications in budo? This is basic common sense, not rocket science.

But if you still think that your martial experience is irrelevant, why don't you just indulge everyone's curiosity? After all, it should only take you a minute. It's not like somebody is asking you to travel to Tibet just to see if it's raining.